Voice conversion techniques for converting speech of one speaker to speech of another speaker have been known (For example, see Patent Document 1 and Non-Patent Document 1).
FIG. 22 shows a basic process of voice conversion processing. The process of voice conversion processing consists of a training process and a conversion process. In the training process, speech of a source speaker and speech of a target speaker who is a target of conversion are collected and stored as speech data for training. Then, training is performed based on the speech data for training to generate a conversion function for converting speech of the source speaker to speech of the target speaker. In the conversion process, the conversion function generated in the training process is used to convert any speech spoken by the source speaker to speech of the target speaker. The above processing is performed in a computer.    [Patent Document 1] JP-A-2002-215198    [Non-Patent Document 1] Alexander Kain and Michael W. Macon “SPECTRAL VOICE CONVERSION FOR TEXT-TO-SPEECH SYNTHESIS”